1. Field of the Invention
The present invention relates to a battery pack that includes a battery unit and a circuit board, and in particular to a battery pack that includes a rectangular battery unit and a circuit board that is arranged on or above an exterior surface of a sealing member or exterior container of the rectangular battery unit.
2. Description of the Related Art
Rectangular rechargeable lithium-ion batteries and polymer batteries have been developed for mobile electronic devices. The rectangular rechargeable lithium-ion batteries typically include a low-profile exterior container, an electrode assembly, a sealing plate, and positive and negative electrode tabs. The low-profile exterior container has a bottom-closed hollow shape. The electrode assembly includes positive and negative electrode plates that face each other, and are accommodated in the exterior container. The opening of the exterior container is closed by the sealing plate. The positive electrode tab extends from the positive electrode plate, and is connected to the sealing plate. The negative electrode tab extends from the negative electrode plate, and is connected to a negative terminal. The negative terminal passes through the sealing plate.
Also, battery packs have been developed and widely used which include a circuit board that is arranged on or above the exterior surface of the aforementioned type of battery unit.
FIG. 6 shows a battery pack that includes a typical rectangular lithium ion battery.
The battery pack shown in FIG. 6 includes a protection circuit in a circuit board 120, and external positive and negative terminals (P24, P26) that are arranged on or above an exterior surface of the circuit board 120. Electric power is supplied through the external positive and negative terminals from the battery pack.
In addition, positive and negative electrode tabs 116 and 117 extend toward a sealing plate 112, and are arranged in parallel to each other in a battery unit.
Also, a positive terminal (P23) and a negative terminal 113 on or above the sealing plate 112 of the battery unit are connected to the circuit board 120 through a connection lead 131 and a lead-equipped safety device 132, respectively. Thus, electric power can be supplied through the circuit board and the external positive and negative terminals from the battery unit to an external circuit (P25).
In the battery pack including the aforementioned battery unit, when electric power is supplied, a current loop is formed from the battery unit to the circuit board, and will produce flux linkage.
The current loop is shown by the lines that connect points of P21 to P33 in FIG. 6.
As shown in FIG. 6, the current loop is formed from the positive electrode plate of the electrode assembly through the positive electrode tab 116 (P21, P22), the positive terminal (P23) on the sealing plate 112, the external positive and negative terminals (P24, P26) on the circuit board 120, wiring (P26 to P29) on the circuit board 120, the lead-equipped safety device 132, the negative terminal 113 and the negative electrode tab 117 to the negative electrode plate of the electrode assembly.
Thus, the formed current loop has a relatively large loop area, which extends from the interior side of the battery unit through the exterior-side circuit board back to the interior side of the battery unit.
This current loop will produce flux linkage. This flux linkage may cause EMI (Electro Magnetic Interference) on a mobile electronic device, which in turn may cause malfunctions of the electronic device.
For this reason, it is required to prevent EMI. In particular, in the case where the output of the battery is high, the flux linkage will be also high. Correspondingly, it is required to prevent EMI.
Japanese Patent Laid-Open Publication No. JP 2003-242,956 A discloses a battery module which addressed this. The battery module includes a plurality of batteries that are connected to each other through bus bars. The plurality of batteries are arranged in particular arrangement, and connected to each other in a particular connection order so as to prevent EMI. The particular arrangement and the particular connection order form a plurality of loop circuits in the connection path. The current flows in the loop circuit adjacent to each other are opposite to each other so that the magnetic fields that are produced by the plurality of loop circuits cancel each other.
This technology is effective at reducing the total strength of the produced magnetic fields, but cannot be applied to battery packs that include one rectangular battery unit that is provided with the circuit as discussed above.
Also, Japanese Patent Laid-Open Publication No. JP 2007-317,668 A discloses a battery pack that includes an electromagnetic wave shielding plate that is arranged along the battery pack. It can be said that this battery pack is effective at preventing EMI. On the other hand, it is also required to suppress electromagnetic waves without such an electromagnetic wave shielding plate in battery packs that are required to be thin or small.
The present invention is aimed at solving the above problems, and its main object is to provide a battery pack that includes a circuit board on an exterior surface of a battery unit but can suppress EMI without an electromagnetic wave shielding plate, and the like.